The present invention relates to a plug for fixing to hollow and to solid building materials. Hollow building materials shall mean, for example, hollow block bricks or panels behind which there is a cavity. Solid building materials shall mean, for example, concrete or similar structures.
Such plugs are known per se they are normally made of plastic material and in a middle region have longitudinally extending expansible limbs that are separated from one another by slots. The expansible limbs are joined to one another at the rear end by a sleeve-form plug end and at the leading end by a sleeve-form plug tip. An expansion screw can be pushed through the sleeve-form plug end and screwed into the plug tip. To fix the plug in a solid building material, the plug is inserted in a hole drilled in the solid building material and an expansion screw is screwed into the plug. The expansion screw presses the expansible limbs apart, that is, the expansion screw expands the expansible limbs, and consequently anchors the plug in the hole drilled in the solid building material.
In a hollow building material or in a panel, the plug is pushed through a drilled hole so that its sleeve-form plug end is located in the hollow building material. An expansion screw is then pushed through the plug end, guided between the expansible limbs and screwed into the plug tip. Screwing the expansion screw into the plug tip causes the plug tip to move towards the plug end, in so doing expanding the expansible limbs. There are actually two known expansion methods. In the first, the expansible limbs buckle outwards as the plug tip moves closer to the plug end and hence form an interlocking engagement with the hollow building material. The other possible method is that the plug tip twists in relation to the plug end as the expansion screw is screwed in, whereby the expansible limbs are wound round each other and form a knot-like structure that interlocks with the hollow building material.
The disadvantage of the known plugs is that the screw is poorly guided and, as it is screwed in, the expansion screw is able to emerge laterally through the slots between the expansible limbs. A further drawback of the known plugs is their low torsional stiffness, which leads to a resilient twisting of the plug tip in relation to the plug end as the expansion screw is screwed in. When screwing in the expansion screw by hand, the resilient twisting of the plug tip in relation to the plug end causes the plug tip, together with the expansion screw is screwed in. When screwing in the expansion screw by hand, the resilient twisting of the plug tip in relation to the plug end causes the plug tip, together with the expansion screw screwed therein, to turn back again when the user lets go of the screwdriver to re-adjust his grip. This has the result that the expansion screw can be screwed into the plug only poorly by hand.